1. Field of the Invention
This invention relates to a resonator for uniformly applying high frequency vibratory energy to a member in contact with the resonator with optimal energy transfer. More in particular, the invention relates to a resonator including an improved piezoelectric transducer.
2. Description of Related Art
In electrophotographic applications such as xerography, a charge retentive surface is electrostatically charged and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder or powder suspension referred to as xe2x80x9ctoner,xe2x80x9d which may be present along with carrier particles in a developer composition. Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced on the charge retentive surface in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface.
The process is well known and useful for light lens copying from an original and printing applications from electronically generated or stored originals, where a charged surface may be imagewise discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a charge retentive substrate operate similarly. In a slightly different arrangement, toner may be transferred to an intermediate surface, prior to retransfer to a final substrate.
Transfer of toner from the charge retentive surface to the final substrate is commonly accomplished electrostatically. A developed toner image is held on the charge retentive surface with electrostatic and mechanical forces. A substrate (such as a copy sheet) is brought into intimate contact with the surface, sandwiching the toner thereinbetween. An electrostatic transfer charging device, such as a corotron, applies a charge to the back side of the sheet, to attract the toner image to the sheet.
The interface between the sheet and the charge retentive surface is not always optimal. Particularly with non-flat sheets, such as sheets that have already passed through a fixing operation such as heat and/or pressure fusing, or perforated sheets, or sheets that are brought into imperfect contact with the charge retentive surface, the contact between the sheet and the charge retentive surface may be non-uniform, characterized by gaps where contact has failed. There is a tendency for toner not to transfer across these gaps. A copy quality defect results.
That acoustic agitation or vibration of a surface can enhance toner release therefrom is known, for example as described in U.S. Pat. No. 4,111,546 to Maret, U.S. Pat. No. 4,684,242 to Schultz, U.S. Pat. No. 4,007,982 to Stange, U.S. Pat. No. 4,121,947 to Hemphill, U.S. Pat. No. 3,653,758 to Trimmer et al., U.S. Pat. No. 4,546,722 to Toda et al., U.S. Pat. No. 4,794,878 to Connors et al., U.S. Pat. No. 4,833,503 to Snelling, Japanese Published Patent Application 62-195685, U.S. Pat. No. 3,854,974 to Sato et al., and French Patent No. 2,280,115.
Coupling of vibrational energy to a surface has been considered in, for example, U.S. Pat. No. 3,635,762 to Ott et al., U.S. Pat. No. 3,422,479 to Jeffee, U.S. Pat. No. 4,483,034 to Ensminger and U.S. Pat. No. 3,190,793 Starke.
Resonators coupled to the charge retentive surface of an electrophotographic device at various stations therein, for the purpose of enhancing the electrostatic function, are known, for example as in: U.S. Pat. No. 5,210,577 to Nowak; U.S. Pat. No. 5,005,054, to Stokes et al.; U.S. Pat. No. 5,010,369 to Nowak et al.; U.S. Pat. No. 5,025,291 to Nowak et al.; U.S. Pat. No. 5,016,055 to Pietrowski et al.; U.S. Pat. No. 5,081,500 to Snelling; U.S. Pat. No. 5,282,005 to Nowak et al.; U.S. Pat. No. 5,329,341 to Nowak et al.; and U.S. Pat. No. 5,493,372 to Mashtare et al.
In addition, resonators for applying vibrational energy to some other member of the device are known, for example as described in U.S. Pat. No. 4,363,992 to Holze, Jr., U.S. Pat. No. 3,113,225 to Kleesattel et al., U.S. Pat. No. 3,733,238 to Long et al., U.S. Pat. No. 3,713,987 to Low and U.S. Pat. No. 5,030,999 to Lindblad et al. U.S. Pat. No. 4,546,722 to Toda et al., U.S. Pat. No. 4,794,878 to Connors et al. and U.S. Pat. No. 4,833,503 to Snelling describe ultrasonic transducer-driven toner transfer for a development system, in which a vibration source provides a wave pattern to move or assist in movement of toner from a sump to a photoreceptor. U.S. Pat. No. 4,568,955 to Hosoya et al. teaches recording apparatus with a developing roller carrying developer to a recording electrode, and a signal source for propelling the developer from the developing roller to the recording media.
In the ultrasonic welding horn art, for example as exemplified in U.S. Pat. No. 4,363,992 to Holze, Jr., where blade-type welding horns are used for applying high frequency energy to surfaces, it is known that the provision of slots through the horn perpendicular to the direction in which the welding horn extends, reduces undesirable mechanical coupling of effects across the contacting horn surface. Accordingly, in such art, the contacting portion of the horn is maintained as a continuous surface, the horn portion is segmented into a plurality of segments, and the horn platform, support and piezoelectric driver elements are maintained as continuous members. For uniformity purposes, it has been desirable to segment the horn so that each segment acts individually.
It has been noted that even with fully segmented horns, as shown in U.S. Pat. No. 5,010,369 to Nowak et al., there is a fall-off in response of the resonator at the outer edges of the device. A similar fall off is shown in U.S. Pat. No. 4,363,992 to Holze, Jr., at FIG. 2, showing the response of the resonator of FIG. 1.
U.S. Pat. No. 5,493,372 to Mashtare et al. describes an imaging device having a non-rigid member with a charge retentive surface moving along an endless path, an imaging system for creating a latent image on the charge retentive surface, a developer for imagewise developing the latent image with toner, a transfer system for electrostatically transferring the developed toner image to a copy sheet, and a resonator for enhancing toner release from the charge retentive surface, producing relatively high frequency vibratory energy and having a portion thereof adapted for contact across the flexible belt member, generally transverse to the direction of movement thereof. The resonator includes a horn member for applying the high frequency vibratory energy to the non-rigid member, having a platform portion, a horn portion, and a contacting portion extending across the non-rigid member. A vibratory energy producing device is coupled to the horn platform for generating the high frequency vibratory energy required to drive said horn member, the vibratory energy producing device including a piezoelectric polymer film material such as polyvinylidene fluoride or composite materials of piezoelectric active ceramic particles randomly mixed throughout a polymer binder (see column 5, lines 13-26). This device does not describe composites or configurations of the present invention.
Current transducer designs in horn assemblies suffer from tip vibration amplitude uniformity problems. Specifically, it is difficult to achieve uniform vibration across the entire surface of the piezoelectric element in the desired vertical direction, known transducer materials used to date exhibiting some degree of undesired transverse vibration. Moreover, current transducer designs also have manufacturing difficulties associated with bonding numerous segments of piezoelectric elements, e.g., lead zirconate titanate (PZT), to the aluminum waveguide of the horn assembly.
What is still sought is an improved piezoelectric element for use in a horn assembly that renders the horn assembly easier and relatively inexpensive to manufacture, as well as exhibits improved uniformity of vibration. This need is particularly strong in the ultrasonic energy applying applications used in electrophotographic printers, where the demand for high quality, electrophotographic printers continues to increase.
It is therefore one object of the present invention to develop a horn assembly and piezoelectric material for use therein that allows for a simplified, cost reduced assembly.
It is a further object of the present invention to develop a horn assembly and piezoelectric material for use therein that achieves more desirable performance, particularly improved vibration uniformity.
These and other objects are obtained by the present invention. In a first aspect, the present invention relates to a resonator for applying vibrational energy to a member, comprising an energy transmitting horn member having a platform portion and a horn portion, the horn portion including a contacting portion for contacting a surface of the member, and a piezoelectric material in association with the horn member for driving the horn member to vibrate, the piezoelectric material responsive to a voltage signal from a voltage source, wherein the piezoelectric material comprises a composite of at least one piezoceramic material and at least one of a polymer or air, and wherein the composite has a 1-3 configuration.
In a second aspect, the invention relates to an imaging apparatus including the resonator. More in particular, it relates to an imaging apparatus comprising at least a non-rigid member with a charge retentive surface moving along an endless path, an image forming station for creating a latent image on the charge retentive surface, a developing station for imagewise developing the latent image with toner, a transfer station for electrostatically transferring the developed toner image to a substrate, and a resonator comprising an energy transmitting horn member having a platform portion and a horn portion, the horn portion including a contacting portion for contacting a surface of the non-rigid member, and a piezoelectric material in association with the horn member for driving the horn member to vibrate, the piezoelectric material responsive to a voltage signal from a voltage source, wherein the piezoelectric material comprises a composite of at least one piezoceramic material and at least one of a polymer or air, and wherein the composite has a 1-3 configuration.
In a further aspect, the invention also relates to a method of making the resonator. In particular, the invention relates to an improved manufacturing process in which the piezoceramic/polymer composite is directly injection molded to the platform portion of the horn member, thereby creating a strong bond in a simple and cost effective manner.
By the selection of a piezoceramic/polymer composite material having the specified configuration for use as the vibratory energy producing source, or transducer, of a resonator, improved piezoelectric material performance is achieved, particularly with respect to control and/or elimination of undesired transverse vibration, and manufacturing complexity is reduced.